Electronics > Projects, Designs, and Technical Stuff
DC load using a CPU cooler
microbug:
Yes, there are PC coolers (e.g., Arctic Cooling 13 Pro) that can do 300W. I imagine there are some that can do more, but CPUs which generate more than 300 watts of heat are generally intended for servers (Intel Xeon). I could switch from the Arctic Cooling 13 to the Arctic Cooling 13 pro - it's only £10 more, but I don't really need the extra power. If I ever do, I can just buy the Arctic Cooling 13 Pro and fit it in place of the old cooler, and change the firmware so it doesn't cut out above 200W.
I just realised that a PSoC would be perfect for this application and would cut down on the number of external components I need. I'll order a PSoC 4100/4200 dev board and take a look (I got a 10% off code for Farnell by email :D)
microbug:
@spikee - how large is the thermal contact on the Freezer 7 (CPU cooler)? I'm wondering how many TO-220 packages I can get under there. I'll probably use either the Freezer 13 or Freezer A30 (17=200W, A30=320W), which (I think) have similar thermal pad sizes.
I'm going to use a different MOSFET to the one I first chose (and stupidly ordered), as the SOA dictates a max of 10V at full current!
EDIT: What would be better thermally: D2PAK packages on the bottom side with thermal stitching, and a cooler on the top; or upside-down TO-220 packages directly touching the cooler?
SeanB:
Upside down TO247 packages are better, lower thermal resistance. Plus you can fit a bigger die inside which has lower resistance to case as well. You probably will only get 9 under the thermal contact, you need a little room to bend the leads and board to attach them to. Use the thickest PCB you can get, otherwise you will need to machine a back brace to get even contact to all 9 dies, otherwise the warping of the board will cause the middle one and the ones not in the corners to not have good thermal contact. A back brace made from thick insulating material with cutouts for the lead stubs will probably be needed in any case, or a thinner one with an aluminum backing plate to give even pressure.
microbug:
OK, thanks. For a back brace, could I use a block of aluminium (6mm thickness, see this eBay listing for source) and drill holes in for the leads? I have a drill press. I could get a thicker aluminium block (1cm for example) if that would be better for the back brace.
Thanks for your help!
SeanB:
Yes, any plate that is stiff, big enough to act as a load spreader and which you can insulate from the board with something like a blank board with milled holes for the leads. You just need it to press evenly on the board so it presses the transistors evenly onto the heat plate.
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